Vertical form/fill/seal (VFFS) packaging systems have proven to be very useful in packaging a wide variety of food and non-food pumpable and/or flowable products. An example of such systems is the ONPACK™ flowable food packaging system marketed by Cryovac/Sealed Air Corporation. The VFFS process is known to those of skill in the art, and described for example in U.S. Pat. No. 4,589,247 (Tsuruta et al), U.S. Pat. No. 4,656,818 (Shimoyama et al.), U.S. Pat. No. 4,768,411 (Su), and U.S. Pat. No. 4,808,010 (Vogan), all incorporated herein by reference in their entirety. In such a process, lay-flat thermoplastic film is advanced over a forming device to form a tube, a longitudinal (vertical) fin or lap seal is made, and a bottom end seal is made by transversely sealing across the tube with heated seal bars. A flowable product is introduced through a central, vertical fill tube to the formed tubular film. The pouch is then completed by sealing the upper end of the tubular segment, and severing the pouch from the tubular film above it. The process can be a two-stage process where the creation of a transverse heat seal occurs at one stage in the process, and then, downstream of the first stage, a separate pair of cooling/clamping means contact the just-formed transverse heat seal to cool and thus strengthen the seal. In some VFFS processes, an upper transverse seal of a first pouch, and the lower transverse seal of a following pouch, are made, and the pouches cut and thereby separated between two portions of the transverse seals, without the need for a separate step to clamp, cool, and cut the seals. A commercial example of an apparatus embodying this more more simplified process is the ONPACK™ 2050A VFFS packaging machine marketed by Cryovac/Sealed Air Corporation.
In some cases, spreader fingers are used commercially on vertical form/fill/seal equipment such as the ONPACK™ 2070A machine. An example is disclosed in Research Disclosure 420056 published Mar. 20, 1999. A removable set of spreader fingers is attached to a support ring, attached in turn to the bottom end of a solids fill tube of an ONPACK™ 2070A vertical form/fill/seal machine, or preferably directly to the fill tube itself. The top ends of the fingers are shaped to allow them to slide through a slot in the support ring or fill tube and, when pivoted down into position, the edges of a slot guide. This supports the fingers, and prevents any unwanted front-to-back movement of the spreader fingers. The top ends of the fingers are forced against the inside of the fill tube and allow the bottom ends of the fingers to be compressed toward the inside of the film tube as required during part of the machine cycle. The spreader fingers can be removed and replaced with fingers of different length, to match different pouch lengths. U.S. Pat. No. 5,038,550 (Wirsig et al.), incorporated herein by reference in its entirety, also discloses at FIG. 5 a pair of spreader fingers used to prepare a tubular film for entry into the space between a pair of sealing jaws. These fingers are typically located above the transverse sealing assembly, but below or at the lower end of the fill tube area of the machine.
Also typical in some VFFS equipment is a pair of squeezing or voiding rollers, e.g. such as shown as reference numeral 15 in FIGS. 1 and 2 of U.S. Pat. No. 6,212,861 (Tsuruta), incorporated herein by reference in its entirety. These rollers, which typically have a smooth, hard rubber or synthetic rubber surface, function to remove fluids, fats, and other food debris from the inside surfaces of the tubular film in an area where a transverse seal is to be made. This allows the transverse seals to be made with less contamination present in the seal area, and results in cleaner and stronger seals. These rollers will typically be disposed on either side of the vertically-sealed tube 48, with appropriate pneumatic or hydraulic means to cycle the pair of rollers towards and away from each other in timed fashion to coincide with the pouch making cycle of the particular machine. The voiding rollers are typically located below the lower end of the longitudinal heat sealing device, and below the lower end of the fill tube that provides food product to the formed pouch, but above the level of the transverse seal bars. Rollers can also be beneficial in that they help flatten the pouch, and form a bottom “stop” to allow for and support the filling of the next pouch in the filling sequence.
Thus, typical of current VFFS equipment is an apparatus with a set of spring steel spreader fingers, below and downstream of which is a set of smooth squeezing rollers.
Unfortunately, the weight of a food product, such as a fluid, inside the pouch being formed in a VFFS system, tends to gather the pouch, thus causing wrinkles immediately after the film advances downwardly from the spreader fingers. The presence of large particulates, such as cubed beef, in close proximity to the longitudinal (vertical) fin or lap seal can also result in wrinkles. The smooth rollers located downstream of the spreader fingers do not alleviate the wrinkle problem.
The presence of such wrinkles can result in defective packages, or at least packages that are unacceptable to the film user or food processor. In certain applications such as retort packaging, any wrinkling of the packaging material, especially of the seal area of the package, is considered unacceptable. This is because the low acid foods typically packaged in retort applications require a hermetic package to avoid food spoilage and ensure a safe food product.
The inventors have found that using a pair of chevron patterned rollers downstream of the pair of smooth rollers removes most of the wrinkles in the tubular film. Alternatively, the chevron patterned rollers can be disposed upstream of the pair of smooth rollers (and downstream of spreader fingers if present), but the improvement in the reduction of wrinkles is less pronounced.
The invention reduces the number of rejects in packages made on VFFS equipment by reducing the percentage of packages with an unacceptable level of wrinkles.